NTSB 787 battery

Published on January 31st, 2013 | By: pwray@ceramics.org

Are you sure you wish to continue?

Do not know root cause of battery failures. Far more serious than people can appreciate. NTSB chair Deborah Hersman: “Fire was present. Signs of thermal runaway and short-circuiting. There are a number of next steps. We are early in our investigation and we have a lot of activities to undertake. ” No specific time table discussed. Dodged question about whether she would feel safe if the 787 was flying again.

New York Times: “Landing the 787 contract was a huge boost for GS Yuasa and for Japan’s efforts in aviation technology. Though not well known outside of Japan, the company describes itself as Japan’s leading manufacturer of batteries and said it had supplied lithium-ion batteries for over 50 satellites “without anomaly or failure.” Still, this was its first effort in commercial aviation. “I had never heard of Yuasa in the aviation context,” Mr. Aboulafia said. GS Yuasa has since been chosen to supply lithium-ion batteries for the International Space Station. Although Pratt & Whitney nominally chose the company, Boeing is the prime contractor on the space station.”

Donald R. Sadoway is the John F. Elliott Professor of Materials Chemistry at MIT. And he is convinced he has a responsibility to help the public understand what is at stake with Boeing’s (BA) 787 lithium-ion battery woes. He also has advice for how Boeing should attack the problem.

In a nutshell, Sadoway thinks that Boeing needs to monitor the temperature and cool each of the eight cells of the 787′s lithium-ion battery or switch to an older battery technology that has a far better safety record – nickel metal-hydride (NiMH).

If Boeing opts to substitute NiMH for lithium-ion, certification could result in delays of up to a year – effectively grounding the 787 until 2014.

Boeing has shipped about 50 787s to airlines around the world including Japan Air, ANA, and United. And it has orders for 848 787s – they were touted as consuming 20% less fuel than competing aircraft – at a list price of $207 million.

But thanks to self-immolating lithium-ion batteries, regulators in Japan and the U.S. have demanded that airlines ground their 787s until the problem with the batteries is solved. In the meantime, a Wall Street analyst recently estimated that Boeing would have to pay at least $550 million to the airlines that are losing business because of the grounded 787s.

So time is certainly money for Boeing shareholders. As Sadoway explained to me in a January 25 interview, the 787 has two lithium-ion batteries – one to provide a surge of current to get the engines started and another to provide backup power in case the main power sources fail.

Sadoway points out that Boeing’s decision to use lithium-ion batteries was very consistent with a core design principle – reduce how much the aircraft weighs so it will cost less to operate. To that end, a lithium-ion battery appears to be an obvious choice because it generates more energy given its weight – 150 watt-hours/kilogram – than any other battery out there.

On that crucial dimension, if lithium-ion batteries are a 3, the next best technology, NiMH is a 2, and a lead acid battery, like the one you use in your car, gets a 1.

But in Sadoway’s view, Boeing made a huge mistake by focusing solely on this dimension when it made the decision to use lithium-ion. Sadoway points out that the lithium-ion battery is far more prone to burning up than these other technologies.

That’s mostly because lithium-ion batteries contain an “organic electrolyte which makes it volatile and flammable.” The two other technologies use a water-based solution which is relatively harmless if it leaks out of the container and is far less prone to spontaneous combustion.

When Sadoway got a look at the lithium-ion battery used in the 787, he was surprised by “the seeming absence of a cooling apparatus.” As he explained, “In a large format battery, heat can be generated faster than it dissipates to the surroundings with the result that the temperature of the battery can rise to dangerously high levels which leads to bloating and ultimately fire.”

The lithium-ion battery in a cell phone, for example, is safer because the battery is so close to the outside of the phone that heat does not build up and cause a problem.

In stark contrast, the 787′s lithium-ion battery is actually eight notebook sized batteries all packed next to each other in a closed box. This means that only the batteries on the ends have any hope of venting the heat they generate. The other six batteries just heat each other up since they can’t release their heat outside the box.

Sadoway does not have access to investigators’ details, however, based on what he has seen, he would urge Boeing to create vents within the box so the batteries can dissipate heat.

He also would put temperature sensors on each of the eight batteries and implement a “system of forced airflow” inside the box to help assure that the temperature of each battery stays below a threshold level.

And once that redesigned battery had been built, he would test the entire thing in a simulated electrical environment that would be about 20% more demanding than its most likely use in the 787′s flight. He would also stress test the battery’s response to changing pressure as the 787 ascends from the runway to 40,000 feet and back.

Sadoway estimates that these changes to the design of the lithium-ion battery would add to its cost. Instead of $1,000 per battery, the cost might rise to $2,000. But that cost would be “peanuts” compared to the $207 million retail price of the 787.

Of course, Boeing might be better off choosing a safer, but less powerful NiMH battery. Sadoway reckons that this battery would have to be 50% heavier – perhaps 37 more pounds – representing 0.01% of the 787′s 502,500 pound weight in order to deliver the burst of current needed to kick-start the 787′s engines.

The problem with using a new battery is that Boeing would have to order Thales, the French company that makes the 787′s electrical system part of which controls the lithium-ion battery, to develop a new control system that would work for the NiMH battery. Sadoway thinks that could take a year to design, build, test, and make safe to fly.

One footnote — Sadoway is puzzled that Boeing’s so-called computerized controls for the lithium-ion battery were considered acceptable. After all, as I wrote, those controls were designed to somehow keep fire or smoke produced by the lithium-ion batteries from getting into the passenger cabin.

As the battery explosions earlier this month demonstrate, the idea that these computerized controls would make the lithium-ion batteries safe for a plane flying 40,000 feet above sea level filled with passengers is inadequate.